1. Technical Field
The present invention relates to a method of satellite status judgment, more particularly, the present invention relates to a method of satellite status judgment according to signal variation slope signals of a satellite.
2. Description of the Related Art
Generally global positioning systems (GPS) employ four positioning satellite operating in coordination with positioning apparatus to position the location of the positioning apparatus. Signals transmitted by a satellite comprises coordinate data of the satellite and transmitting time of each signal, and positioning chip in the positioning apparatus employs the signals to calculate the location of the positioning apparatus.
When a GPS employs four satellites to position, any one satellite is affected would result in a positional error in three-dimension space. One reason of satellite signal errors is probable external mask of landform interferes with satellite signals being transmitted to the positioning apparatus. Relative positions of the four selected satellites to the positioning apparatus may affect GPS positioning effect.
No matter Satellite Based Augmentation Systems (SBAS), Assisted Global Positioning System (AGPS), or Differential Global Positioning System (DGPS), have a common problem that the satellite signals can be provided only when the users is near the base station or in an available region covered by satellite signals. When the satellite signals are masked, the systems would not perform well because of affection of signal strength.